I am a 23 year old engineer with a degree in Manufacturing Engineering Technology.

We are partial to Mobile Home parks and migh suggest learning a bit more about them if this is of interest to you, then join your local manufactured home industry association in your area.  

Even if We know that Bayou City is facing the oil slump very hardly, but there niche and part of the town that still performing well because are occupied by different types of professionals figure that are working in sector like maritime transport, medical, manufacturing and distribution.My suggestion is to study the market, contact a local agent, read the news, and then make your decision based on real number and real prospective and area development.Once again, depending everything on what Submarket your are going to focus.

In many parts of the US, manufacturing and similar jobs are going away and what remains are service sector jobs.

Do not, do not, do not allowed someone who is not a licensed professional to install the furnace, it will invalidate the warranty.The warranty should be able the same from every manufacturer, so you're pretty much even there.I wouldn't necessarily recommend flex duct, it is cheaper, but you can end up with integrity issues, even in the short run.My best suggestion is to find an HVAC supplier, and check to see what the prices are for furnaces ... this will absolutely open your eyes as far as material costs are concerned.  

have seen homes on similar size lots go for around 150k. the land is just sitting there for several years going on decades. the shrubs seem to be well on their way into growing into trees; is there like a service that clears lots for a fee, or maybe it would be more cost effective to put a (manufactured?)

The property is a huge piece of land with a 1990 manufactured home.

You acquire, fix the issue thereby adding value, properly market, and sell for top dollar (relatively).But, if your answer is an external factor beyond possible repair (general area, the manufactured/trailer homes a block away, the major highway with retail/industrial vibe a block in the other direction, etc.), then you're probably better off moving on to the next one.  

It currently has only a manufactured home on it.

There is also the option of joining the Texas Manufactured Housing Association.